Tribological behaviors of hierarchical porous PEEK composites with mesoporous titanium oxide whisker

doi:10.1016/j.wear.2012.10.008

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Volume 297, Issues 1–2, 15 January 2013, Pages 736-741

https://doi.org/10.1016/j.wear.2012.10.008 Get rights and content

Abstract

Hierarchical porous PEEK self-lubricating composites were prepared by mold-leaching and vacuum melting process under high temperature. The tribological behaviors were investigated for the porous PEEK composite and the porous composite after incorporating micro-porogen (NaCl) and mesoporous titanium oxide whiskers. If only micro-porogen was incorporated, the lowest steady state specific wear rate was observed for PEEK composites filled with 30% NaCl. Based on this porous PEEK composite, the effects of mesoporous titanium oxide whiskers and non-perforated titanium oxide whiskers on the friction and wear properties of PEEK composites were studied. Results showed that nano-micro porous PEEK composites with 30 wt% micro-porogen and 5 wt% mesoporous titanium oxide whiskers reached the lowest friction coefficient and specific wear rate, which were recorded as 0.0194 and 2.135×10^–16 m³/Nm under the load of 200 N. Compared with 15 wt% carbon fiber-reinforced PEEK composite which is widely used in industry, the wear resistance of the designed hierarchical porous PEEK composite increased by 41 times, showing outstanding wear resistance.

Highlights

► Porous PEEK composites were prepared by mold-leaching and vacuum melting process. ► Grease exuded from hierarchical pores and form uniform lubricating film on worn surface. ► The porous PEEK composites own low friction and outstanding wear resistance.

Introduction

PEEK (polyetheretherketone) is an important engineering material. As a typical high performance semicrystalline thermoplastic polymer, PEEK has received significant attentions in recent years due to its high mechanical strength and elastic modulus, satisfied combination of thermal and mechanical properties, chemical inertness, high toughness, easy processing, high wear resistance and low friction coefficient [1], [2], [3]. Recently, the research on the manufacturing and investigation on friction and wear properties of PEEK and its composites have attracted more interest, and PEEK has become prevalent in the areas of engineering plastics and tribology [4]. Many researchers have modified PEEK to enhance its mechanical and tribological properties by fiber-reinforcing, organic-blending, inorganic micron- and nano-filling. Previous literatures focusing on the tribological properties of PEEK have been mainly done by the groups of Friedrich [5], Burris [6], Bahaduer [7] and Briscoe [8].

With the rapid development of modern technology, high performance PEEK composites with advanced tribological properties are in urgent demand. However, the high friction coefficient and wear rate of pure PEEK and PEEK composites are the main obstacles for their wider applications under high load, velocity and temperature [9]. Nevertheless, porous self-lubricating structural design based on PEEK matrix could be a promising alternative for economical, ecological and technical concerns. The porous structure is able to uptake grease lubricant. During tribological testing, the grease will be squeezed out of the porous structure under the loaded pressure, and will be exuded well on the sliding surface with the effect of generated friction heat. Then, grease lubricating layers can be formed on friction surface for a long working period with low friction and high wear resistance [10]. Some efforts have been made to investigate the effect of internal solid and/or oil lubricants on tribological behaviors of porous polyamide (PA)[11], polyimide (PI) [12] and ceramics [13]. However, to the best of our knowledge, no literature is available regarding hierarchical porous polymers for tribological applications.

In this study, an attempt has been made to develop an effective processing technique and evaluate the feasibility of using NaCl, mesoporous titanium oxide whisker and non-perforated titanium oxide whisker as fillers for PEEK. The aim of this work is to develop a preparation method for a new self-lubricating material—hierarchical porous PEEK material impregnated with lithium-base grease and to study their tribological properties.

Section snippets

Materials and preparation of the PEEK composites

PEEK powder in 160-mesh size (supplied by Jilin University High-Technology CO. LTD, Changchun, China), was used as the polymer matrix material. Sodium chloride was sieved, which plays the role of pore-forming agent. Mesoporous titanium oxide whisker (M–TiO₂–W, as shown in Fig. 3) (supplied by the College of Chemical engineering, Nanjing University of Technology) was synthesized from the sintered K₂Ti₂O₅, which involves a novel hydrolytic step for the mesoscopic microphase separation [14]. The

XRD and BET comparison of the M–TiO₂–W and N–TiO₂–W

Fig. 1 shows the X-ray diffraction pattern of TiO₂ whiskers. It can be seen that the diffraction peaks of TiO₂ whisker are completely consistent with the characteristic diffraction peaks of the anatase TiO₂. Meanwhile, no diffraction peaks of other crystalline TiO₂ or other substances were found. Therefore, the mesoporous titanium whiskers and non-porous titanium whiskers are mainly anatase TiO₂.

The pore structure parameters of the sample such as the surface area, pore size and pore volume are

Conclusions

(1)
Self-lubricating PEEK composite has been prepared by molding-leaching and vacuum melting process under high temperature. The lowest friction coefficient and specific wear rate were obtained using micro-porous PEEK composite filled with 5 wt% M–TiO₂–W and impregnated lithium-base grease, which were 0.0194 and 2.135×10⁻¹⁶ m³/(Nm) under the load of 200 N, respectively.
(2)
Compared with 15 wt% CF/PEEK composite which is widely used in industry, the wear resistance of the designed hierarchical porous PEEK

Acknowledgments

The research is financially supported by the National Science Foundation of China (Grant nos. 50903010 and 51175066), FANEDD (201164), the New Century Excellent Talent (1251-NCET-007), the National Doctor Foundation (20110490114), the Provincial Core Teachers (gg1203) and the Provincial Doctor Foundation (bh2010xx).

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Tribological behaviors of hierarchical porous PEEK composites with mesoporous titanium oxide whisker

Abstract

Highlights

Introduction

Section snippets

Materials and preparation of the PEEK composites

XRD and BET comparison of the M–TiO2–W and N–TiO2–W

Conclusions

Acknowledgments

Composites Science and Technology

Composites Science and Technology

Wear

Tribology International

Wear

Wear

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XRD and BET comparison of the M–TiO₂–W and N–TiO₂–W